Coosa board for SF20
 

Hi all,

I am debating on going with coosa vs a pourable type of composite for my transom on my 69 SF20.

As far as I can tell coosa does not sell a board at 5/8in. I can get two at 3/4 or one at 3/4 and one at 1/2. Being i'm using coosa over traditional ply could I get away with using a 1.5in core and not adding so much glass to the inside skin (I'm building from the outside) I also don't need the thickness of the layer to laminate the ply's together.

The plywood that came out of the transom was two pieces of 3/4, so it was redone over the years but the inner skin of my transom was paper thin, ideally I would have one at 3/4 and one at 5/8 so I can add to the inner skin but I would rather use a composite over traditional plywood.

OR I could beef up the inner skin build the outer skin and pour in some ARJAY and be done with it. The only problem is i'm trying to get quotes to ship the stuff to NJ and i'm guessing it's not going to be cheap, it also is heavier than coosa and I have no intentions of raising my deck. Coosa on the other hand I can probably pick up as compositesone in NJ and have it by the weekend.

Seems I just found 5/8 listed from a different distributor, I guess I didn't search hard enough

I would match core thickness after beefing up the inner skin. The outer skin being off already means youre glassing and fairing anyhow so build that up as much as you want...

I only saw 1 pic on that link, can ya take some more??

These are the only ones on my phone, I can snap more when I?m home. I really screwed my self by not leaving a lip for the scarf, I really just attacked the transom without thinking of leaving more room until I stepped back to look at it lol.
The plywood there is a sample of what came out.

The new transom will be composite either pourable or coosa.

Last question! I’m back to square one, coosa is hard for me to find, but my local fiberglass supply has Penske in 1/2 and 3/4 with not 5/8 option. I would like to give them my business. Would putting two in at 3/4 or one at 3/4 and one at 1/2 be an option for me if I add extra glass in the end? What’s everyone’s thoughts on that? Two at 3/4 came out with a thin inner skin, if I put two 3/4 Penske it can’t be any worse than what came out right?

I'm assuming you don't want to work from the inside of the boat, so if your options are 1.25" core plus a lot more inner skin glass or only 1.5" core, I'd go with building up the inner skin and a thinner core. Penske (or any structural foam) has a fraction of the compressive strength of plywood, so you'll want the extra glass on the inside to help distribute your outboard's fastener load.

The problem now is tying the outer skin back into the hull. Without a total deconstruction of the inner skin youre kinda stuck with beveling and tabbing the outer skin to the outside of the hull. If youre doing that, the thickness doesnt have to fit back into what was originally there, you can build it to whatever you wanted.

So use two at 3/4 destroy whatever lip I have remaining on the outside and wrap around to the hull sides? I’m ok with that as I was thinking of painting the hull in the future anyway, and it will allow me to get a 12:1 scarf. I think I have to wrap to the hillsides anyway I really screwed that one up! So many ways to skin this cat.

The sides aren't really a problem, other than fairing it out to look good. If you have to wrap around the bottom though, that'll create a hook that could cause real performance problems.

Good point, it could be tough to get that right. I will measure the lip I left, I know if my laminate is 1/4 in thick 12:1 would be a 3 in scarf I will measure and check if I have that.

Have you looked for Baltek? That's what I used in my 18...1 layer of 1.5". However, I did mine from the inside. The transom is rock solid and I couldn't be happier. I'll have to beg to differ on the compression strength comment versus plywood. This stuff has tremendous compression strength!

I didnt see much of a lip left for enough to tab into. I would wrap 10" or so onto the hull. Like was said make sure you bevel enough so you dont build up a lump with glass on the bottom...

The local fiberglass supply had Penske so I went with the Penske board 2 at 3/4. I cut the lip out completely as I already had to wrap around anyway and went with existing inner skin laminated to 1.5 oz, 1708, 1708, 1.5 0z, 3/4 Penske, 1.5oz, 3/4 penske. I have decent access to the inside of the transom right now through the fish boxes, I may tab in some 1708 on the inside as well or even get rid of the boxes all together to work more on the inside still haven’t decided yet.

This weekend I’m going to fair the outside up the hull sides and was thinking of this laminate schedule for the outer skin and looking for thoughts

Outside layer of Penske board —>1.5oz, 1708,1708,1708,1708,6oz cloth wrapped to the hull sides.

I already started fairing the bottom of the hull to accept new glass, what a PITA I don’t recommend going this route haha!

The enclosure I built is small so backing up to take pictures to see the whole thing at this point is impossible